1. Field of the Invention
The present invention relates to a motor-and-pump assembly, in particular for providing pressure for a brake actuating device of a motor vehicle brake system.
2. Description of the Related Art
To make vacuum available for a pneumatic brake booster whose interior is subdivided into at least one vacuum chamber and one working chamber, vacuum pumps are typically employed which aspirate residual air out of the vacuum chamber and exhaust it into the atmosphere. Vane-type pumps or wing pumps are typically used for this purpose in the automotive industry. Due to their principle, these pumps suffer from much friction and need lubrication in order to reach an acceptable useful life. Vacuum pumps with vanes which are driven by the internal combustion engine of the motor vehicle are therefore connected to the oil circulation of the internal combustion engine. Nevertheless, an appreciable portion of the power output by the internal combustion engine is required for driving a pump of this type. And this is even necessary when the vacuum in the chamber to be evacuated is already fully developed. Therefore, it is appropriate to operate the vacuum pump with electric energy and to switch it on only when the absolute pressure in the vacuum chamber rises in excess of a predetermined value.
Furthermore, it is possible in vehicles with electric or hybrid drive that the vacuum pump is not operated at all or is not operated temporarily by the internal combustion engine. For this reason, electrically driven vacuum pumps are used in these vehicles.
It may involve great expenditure to equip such an electrically driven pump with a lubricant cycle or to connect it to such a cycle. Therefore, only dry running vacuum pumps lend themselves to being used in motor vehicles with brake systems equipped with an electrically driven vacuum pump. To this end, the self-lubricating material graphite is employed in vane-type pumps, and the vanes are made from this material with the necessary precision and requiring great expenditure. Therefore, efforts are directed to the use of a diaphragm pump for the electric supply of brake vacuum.
Diaphragm pumps are generally known. Document DE 35 29 978 A1 discloses a motor-and-pump assembly comprising a double diaphragm pump with a rotating eccentric shaft which is driven by an electric motor.
The automotive industry places very high demands on the acoustic comfort of the motor vehicle components and requests from its suppliers robust, long-lived pumps with very low noise emissions. These requests cannot be satisfied by the prior art diaphragm pumps due to vibrations or necessitate great expenditure in sound absorbing measures, respectively.
It is an object of the invention to provide a motor-and-pump assembly which comprises a dry-running pump and satisfies the high demands with respect to the acoustic comfort. Another objective of the invention is directed to improving the motor-and-pump assembly in terms of its pump effect.